Replace alert()/confirm() UX with native toast notification system

[shadowbipnode]

Goal
Modernize browser UX by replacing blocking dialogs with elegant toast notifications.

Current issue
Some flows still use:

• alert()
• confirm()
• blocking dialogs

This feels outdated and breaks UX consistency.

Tasks

• Create global toast system
• Success/info/error/warning variants
• Auto-dismiss animations
• Queue multiple notifications
• Integrate with:
  • popup blocking
  • permissions
  • wallet actions
  • updates
  • downloads

Acceptance criteria

• No raw alert() dialogs remain
• Toasts match browser theme
• Notifications feel native and modern